Refrigeration apparatuses each includes an outdoor unit such as a condensing unit, and an indoor unit installed in a to-be-cooled space such as a cooler or a showcase. In general, the outdoor unit includes a compressor and a condenser, and the indoor unit includes an expansion valve and an evaporator. That is, in the refrigeration apparatuses, the compressor, the condenser, the expansion valve and the evaporator are connected by refrigerant pipes to form a refrigerant circuit.
Generally, in a refrigeration apparatus, an outdoor unit and an indoor unit are selected separately. To be more specific, for a refrigeration apparatus, outdoor and indoor units manufactured by different manufacturers are selected separately and used in combination. Furthermore, there can be a plurality of combinations of outdoor and indoor units. For example, a given outdoor unit can be combined with each of a plurality of indoor units manufactured by different manufacturers. Specifically, an outdoor unit may be combined with an indoor unit manufactured by a given manufacturer, or may be combined with an indoor unit manufactured by another manufacturer. Thus, in order to ensure that whatever indoor unit is combined with the outdoor unit, they can be handled, the outdoor unit needs to be independently controllable regardless of what indoor unit is combined with the outdoor unit.
As an example of independent control by the outdoor unit, the following independent control is present: the operation frequency of a compressor and the rotation speed of a fan which sends air to a condenser are changed such that an evaporation temperature obtained by subjecting a suction pressure detected by the outdoor unit to saturation conversion is set to a target evaporation temperature set to a fixed value which is lower than, for example, a target interior temperature by 10 degrees C. However, in a control to be performed, with the target evaporation temperature set to the fixed value, it is not possible to set an appropriate target evaporation temperature in accordance with a load variation in the to-be-cooled space. Consequently, even when a load is low, the operation frequency of the compressor unnecessarily rises.
As an apparatus which solves the above problem, conventionally, a refrigeration apparatus in which setting of a target evaporation temperature in an outdoor unit is variable is known. In such a refrigeration apparatus, a controller of the outdoor unit obtains, using a communication unit, information indicating a load state of an indoor-unit side, and changes the setting of the target evaporation temperature based on the obtained information. Furthermore, in other known refrigeration apparatuses, a controller of an outdoor unit obtains a target evaporation temperature calculated based on a load state of an indoor-unit side, and performs updating based on the obtained target evaporation temperature (see, for example, patent literatures 1 to 5).
Patent literatures 1 and 2 each disclose a method for setting a target evaporation temperature based on the difference between an interior temperature and a target interior temperature. Patent literature 3 discloses a method for setting a target evaporation temperature based on the difference between a target interior temperature and an interior temperature and the difference between a target evaporation temperature and an evaporation temperature. Patent literature 4 discloses a method for correcting a target evaporation temperature based on an interior temperature gradient. Patent Literature 5 discloses a method for adjusting a target evaporation temperature based on wetness of sucked refrigerant.